Unlockable Mii Costumes:
Unlock the following costumes for your Mii by performing the corresponding tasks:

Charmy Costume - Play for over one hour.
Chip Outfit - Play for over 5 hours.
Cream Outfit - Get 1st Place in 10 London Party Bonus Games
Espio Costume - Come in 1st Place 10 times.
Iggy Suit - Play as a Mii in 50 Events
Larry Suit - Answer 10 questions right in London Party quizzes.
Super Sonic Suit - Get 50 1st places
Wendy Koopa Outfit - Play as a Mii in 10 Events
Werehog Suit - Come in 1st Place 25 times.